Goldens makes a glazing medium. It works well with both heavy and open. I could never get it to work well with the fluids, but that may be me. Actually, I used more gloss medium than glazing medium. You have to check the label of whatever medium you use - glazing, soft gel, gloss medium... some of these can be thinned a ton, but others say no more than 25% or 50% compared to the actual paint and / or paint and water. If you thin your pigment too much, it can not bond on the surface and will flake off when you try to paint another layer on top.
Heavy are quick drying. Opens stay wet a day or two and are easier to make smooth, gentle blends, because you can still move the paint around.
One or two glazes will work in acrylics, but not more. Light goes through to next layer and comes back at you,. But the layers are plastic, and acting as plastic, they do not have real transparency, even when adding mediums. Oils are transparent, and become more transparent over time, so there is much more glazing possibilities; many more layers, more subtle.... I do not say you should not use acrylics. I used acrylics for 25 years, LOVED them, but when I really needed to glaze I needed to switch to oils.